Integrated process utilizing nitrogen and carbon dioxide streams for enhanced oil recovery

ABSTRACT

Disclosed is an integrated enhanced oil recovery process and system for use in recovering relatively light oil from an oil-producing reservoir utilizing the injection of nitrogen produced by air separation in a cryogenic air separation unit and/or carbon dioxide produced by combustion in an oxygen fired steam generator fed by oxygen from the air separation unit. The steam produced may be utilized for suitable uses other than injection into an oil-producing reservoir, including heat generation and driving steam turbines, which in turn drive rotary equipment such as electrical generators, pumps and compressors.

BACKGROUND

The present disclosure relates to the generation of gases for enhancing the recovery of oil from a reservoir. More particularly, the disclosure relates to the integration of an air separation unit and an oxygen-fired steam generator to produce nitrogen and carbon dioxide streams for use in enhanced oil recovery.

Processes for enhancing the recovery of oil from an oil-producing reservoir, referred to as enhanced oil recovery (EOR) processes, may involve the injection of steam or gas into the reservoir. The steam or gas improves the flow characteristics of the oil in order to facilitate production. When the oil to be produced is heavy oil, e.g., having an API gravity of between about 10 and about 20, steam is appropriate for injection. When the oil to be produced is relatively light, e.g., having an API gravity of between about 25 and about 50, steam is not normally appropriate for injection, but rather a gas which is miscible with the oil is used, such as nitrogen or carbon dioxide. Either nitrogen or carbon dioxide may be preferred depending on the reservoir, the type of oil being produced and the availability of the nitrogen or carbon dioxide. If available and economic, carbon dioxide from natural reservoirs is generally utilized for EOR. The high cost of capturing carbon dioxide from anthropogenic sources has been a strong deterrent for this source of CO₂ for EOR. Nitrogen for injection in an EOR process is also costly since the nitrogen is generally provided by nitrogen generation plants.

It would be desirable to have an economic EOR process and system for use in recovery of relatively light oil utilizing nitrogen and carbon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where:

FIG. 1 is a schematic drawing of an integrated process according to one embodiment in which a nitrogen stream and a carbon dioxide stream are generated for use in enhanced oil recovery.

SUMMARY

According to one embodiment, a process for enhanced oil recovery process is provided. The process includes feeding air to a cryogenic air separation unit, operating the cryogenic air separation unit to produce an oxygen stream and a nitrogen stream, feeding the oxygen stream, water and a fuel to an oxygen fired steam generator, combusting the fuel in the oxygen fired steam generator to produce steam and a carbon dioxide stream, utilizing the steam for a use other than injection into an oil-producing reservoir, compressing at least one of the carbon dioxide stream and the nitrogen stream to form an injection gas stream, and injecting the injection gas stream into at least one oil-producing reservoir.

According to another embodiment, a system for enhanced oil recovery is provided. The system includes a cryogenic air separation unit having an air inlet, and oxygen outlet and a nitrogen outlet, an oxygen fired steam generator in fluid communication with the oxygen outlet of the cryogenic air separation unit and further having a fuel inlet, exhaust gas outlet and steam outlet, the steam outlet being in fluid communication with equipment selected from the group consisting of a steam turbine, a heater and a boiler, a means for carbon dioxide dehydration and purification, a compressor for compressing at least one of the carbon dioxide stream and the nitrogen stream to form an injection gas stream, and a means for injecting the injection gas stream into an oil-producing reservoir.

DETAILED DESCRIPTION

According to one embodiment, a process for enhanced oil recovery process is provided in which a cryogenic air separation unit is operated to transform a feed of air to an oxygen stream and a nitrogen stream. The oxygen stream, water and a fuel are fed to an oxygen fired steam generator in which the fuel is combusted to produce steam and a carbon dioxide stream. In one embodiment, the fuel is primarily methane. The oxygen stream contains at least 90% oxygen, even at least 95% oxygen and even at least 97% oxygen. Higher purity oxygen will result in a higher purity carbon dioxide stream.

The steam is utilized for any suitable use other than injection into an oil-producing reservoir. In one embodiment, the steam is fed back to the air separation unit to drive steam turbines that are directly linked to compressors within the air separation unit. In one embodiment, the steam is used to generate power, for example, by driving a turbine in a power generation unit. In one embodiment the steam is used to drive steam turbines that are directly linked to other rotary equipment, such as pumps and compressors. The power generated can be used for any convenient purpose, including motor-driven air separation unit compressors. In one embodiment the steam is used to provide process heat via a heat exchanger, with the steam condensing on one side of the heat exchanger and the process fluid heating up on the other side of the heat exchanger.

Either the carbon dioxide stream produced by combustion in the oxygen fired steam generator or the nitrogen stream produced by air separation in the cryogenic air separation unit can be compressed to form an injection gas stream which is injected into an oil-producing reservoir to enhance oil recovery. The injection gas stream is compressed to a pressure between about 1 psi and about 20,000 psi for injection. If either the carbon dioxide stream or nitrogen stream is not used as an injection gas stream to enhance oil recovery, it may be stored, transported, subjected to further transformation and/or vented to the atmosphere.

The carbon dioxide stream is preferably dehydrated prior to compression. The carbon dioxide stream can also be purified as needed to remove substituents such as, for example, nitrogen, argon and/or oxygen.

FIG. 1 illustrates one embodiment of a system for carrying out an enhanced oil recovery process. A feed of air 2 is fed to a cryogenic air separation unit 20 through an air inlet. An oxygen stream 4 exits the air separation unit through an oxygen outlet and nitrogen stream 7 exits the air separation unit through a nitrogen outlet. The oxygen stream 4 is delivered to an oxygen fired steam generator 10 in fluid communication with the oxygen outlet of the cryogenic air separation unit. The steam generator 10 receives fuel 1 through a fuel inlet and water 8 through a water inlet. As a result of the heat of combustion and actual combustion within the steam generator 10, steam 3 and exhaust in the form of water and carbon dioxide stream 6 are formed, respectively. The bulk of the water is condensed out in condenser 40 as water stream 11. The remaining carbon dioxide stream 9 is formed.

The cryogenic air separation unit 20 can include at least one steam turbine driven compressor in fluid communication with the steam outlet from the steam generator 10 such that the compressor is driven by steam 3. Steam 3 can also be used to drive other rotating equipment. For instance, steam 5 can be diverted to drive a power generation unit 30. Power produced by the power generation unit 30 can be used in any convenient way, including providing power to motors which drive the compressors of air separation unit 20.

In one embodiment, carbon dioxide stream 9 can be dehydrated and/or purified prior to compression. The carbon dioxide stream can then be compressed to form an injection gas stream for injection into an oil-producing reservoir 50 a. Dehydration can also take place in a compression train.

Likewise, nitrogen stream 7 can be compressed to form an injection gas stream for injection into an oil-producing reservoir 50 b. Carbon dioxide stream 9 or nitrogen stream 7 can be injected into an oil-producing reservoir to enhance oil recovery.

In one embodiment, both the carbon dioxide and nitrogen streams are injected, sequentially, injecting the carbon dioxide stream first, followed by the nitrogen stream, or vice versa, depending on the specific conditions of the reservoir. For example, in order to facilitate recovery of oil from a reservoir, nitrogen may be first injected to pressurize the contents of the reservoir, and carbon dioxide may be then injected to combine with the oil. In another embodiment, the carbon dioxide stream is injected into one oil-producing reservoir and the nitrogen stream is injected into a separate oil-producing reservoir in a separate location.

Unless otherwise specified, the recitation of a genus of elements, materials or other components, from which an individual component or mixture of components can be selected, is intended to include all possible sub-generic combinations of the listed components and mixtures thereof. Also, “comprise,” “include” and its variants, are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that may also be useful in the materials, compositions, methods and systems of this invention. 

1. An enhanced oil recovery process, comprising: a. feeding air to a cryogenic air separation unit; b. operating the cryogenic air separation unit to produce an oxygen stream and a nitrogen stream; c. feeding the oxygen stream, water and a fuel to an oxygen fired steam generator; d. combusting the fuel in the oxygen fired steam generator to convert the water to steam and produce a carbon dioxide stream; e. utilizing the steam for a use other than injection into an oil-producing reservoir; f. compressing at least one of the carbon dioxide stream and the nitrogen stream to form an injection gas stream; and g. injecting the injection gas stream into a first oil-producing reservoir.
 2. The process of claim 1, further comprising compressing the other of the carbon dioxide stream and the nitrogen stream to form a second injection gas stream; and injecting the second injection gas treatment into a second oil-producing reservoir.
 3. The process of claim 1, wherein the steam is utilized to drive steam turbines which in turn drive compressors in the air separation unit.
 4. The process of claim 1, wherein the steam is utilized to generate power.
 5. The process of claim 4, further comprising utilizing the power to drive motor-driven compressors in the air separation unit.
 6. The process of claim 1 wherein the oxygen stream comprises at least 90% purity oxygen.
 7. The process of claim 1, further comprising dehydrating the carbon dioxide stream.
 8. The process of claim 1, further comprising purifying the carbon dioxide stream prior to the compressing step.
 9. The process of claim 1 wherein the injection gas stream comprises carbon dioxide, further comprising compressing the nitrogen stream to form a second injection gas stream and injecting the second injection gas stream into the first oil-producing reservoir.
 10. The process of claim 1 wherein the injection gas stream comprises nitrogen, further comprising compressing the carbon dioxide stream to form a second injection gas stream and injecting the second injection gas stream into the first oil-producing reservoir.
 11. A system for enhanced oil recovery, comprising: a. a cryogenic air separation unit having an air inlet, and oxygen outlet and a nitrogen outlet; b. an oxygen fired steam generator in fluid communication with the oxygen outlet of the cryogenic air separation unit and further having a fuel inlet, water inlet, exhaust gas outlet and steam outlet, the steam outlet being in fluid communication with equipment selected from the group consisting of a steam turbine, a heater and a boiler; c. a means for carbon dioxide dehydration; d. a compressor for compressing at least one of the carbon dioxide stream and the nitrogen stream to form an injection gas stream; and e. a means for injecting the injection gas stream into an oil-producing reservoir.
 12. The system of claim 11 wherein the cryogenic air separation unit comprises at least one steam turbine driven compressor in fluid communication with the steam outlet. 